Subject: bug#32728: bug#32729: Xemacs 23 times as fast as GNU Emacs

From: "Benninghofen, Benjamin Dr." <[email-masked]>
Date: Fri, 25 Oct 2019 06:38:16 +0000

For me your discussion about the performance problem appears very theoretical.
Why do you not just compare the relevant GNU Emacs Source Code with the Xemacs Source Code?

Benjamin Benninghofen

-----Original Message-----
From: Lars Ingebrigtsen [mailto:[email-masked]] 
Sent: Monday, October 14, 2019 10:54 AM
To: Eli Zaretskii
Cc: [email-masked]; [email-masked]; Benninghofen, Benjamin Dr.; [email-masked]
Subject: Re: bug#32729: Xemacs 23 times as fast as GNU Emacs

Actually, my benchmarking is somewhat wrong.

start-process with a filter, but discard output:

(let ((coding-system-for-read 'binary))
  (kill-buffer (get-buffer-create " *zeroes*"))
  (benchmark-run
      1
    (let ((proc (start-process "dd" (get-buffer-create " *zeroes*") "dd"
			       "if=/dev/zero" "bs=4096" "count=250000")))
      (set-process-filter proc (lambda (proc string)))
      (while (and (process-live-p proc)
		  (accept-process-output proc 1))))))
=> (18.828236636 59 13.315468088000017)

filter, but insert the output:

(let ((coding-system-for-read 'binary))
  (kill-buffer (get-buffer-create " *zeroes*"))
  (benchmark-run
      1
    (let ((proc (start-process "dd" (get-buffer-create " *zeroes*") "dd"
			       "if=/dev/zero" "bs=4096" "count=250000")))
      (set-process-filter proc (lambda (proc string)
				 (with-current-buffer (get-buffer " *zeroes*")
				   (goto-char (point-max))
				   (insert string))))
      (while (and (process-live-p proc)
		  (accept-process-output proc 1))))))
=> (21.120281346 59 13.250166416000013)

With the default filter:

(let ((coding-system-for-read 'binary))
  (kill-buffer (get-buffer-create " *zeroes*"))
  (benchmark-run
      1
    (let ((proc (start-process "dd" (get-buffer-create " *zeroes*") "dd"
			       "if=/dev/zero" "bs=4096" "count=250000")))
      (while (and (process-live-p proc)
		  (accept-process-output proc 1))))))
=> (34.046986424 116 26.025843717999976)

(!)

So the default filter is really slow?

Anyway, compare with call-process:

(let ((coding-system-for-read 'binary))
  (kill-buffer (get-buffer-create " *zeroes*"))
  (benchmark-run 1 (call-process "dd" nil (get-buffer-create " *zeroes*") nil "if=/dev/zero" "bs=4096" "count=250000")))
=> (1.694743653 0 0.0)

So what makes start-process 10x slower than call-process?  If it is all
the string creation before calling the filters, default or not, then my
point stands, but this obviously requires a more in-depth dive into
process.c.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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